Cement in signal box shuts London subway line

A major line on the London Underground was largely shut down Thursday after fast-setting concrete leaked into signaling equipment.

Subway operator Transport for London initially identified the cause of the problem on the Victoria Line as "flooding." But London Underground later said contractors working on a new station had leaked water and cement into a signal control room, damaging equipment.

Operations director Nigel Holness said most of the line was shut and service was unlikely to return to normal before Friday.

The London subway system, the world's oldest, sees about 3.5 million journeys each day.